Vertical track zoning for disk drives

ABSTRACT

A method of defining storage format in a data storage device having a plurality of storage media and a plurality of corresponding data transducer heads, each transducer head for recording on and playback of information from a corresponding storage medium. A storage format is defined in at least one region on each storage medium, wherein each region includes a plurality of concentric tracks for recording on and playback of information. The method includes: moving each storage medium with respect to the corresponding transducer head and reading data from each storage medium with the corresponding transducer head; measuring a record/playback performance capability of each transducer head; selecting a group of track densities, one track density for each region on a storage medium, based on the measured record/playback performance capability of the corresponding transducer head.

RELATED APPLICATION

[0001] Priority is claimed from U.S. patent application Ser. No.10/053,220 filed Jan. 17, 2002, which is incorporated by referenceherein in its entirety.

FIELD OF THE INVENTION

[0002] The present invention relates generally to the storage ofinformation on storage media, and more particularly to storage ofinformation on rotating magnetic media such as disks in a disk drive.

BACKGROUND OF THE INVENTION

[0003] Data storage devices such as disk drives are used in many dataprocessing systems for data storage. Typically a disk drive includes amagnetic data disk having recording surfaces with concentric datatracks, and a transducer head paired with each recording surface, forwriting data to, and reading data from, the data tracks. Each pairedmagnetic head and media surface couples to provide a unique datarecording capability which depends on the fly height of the head fromthe recording surface, the quality/distribution of magnetic media on therecording surface, and the magnetic properties of the magnetic head.

[0004] Conventional methods of recording data using the paired head andrecording surface are inefficient because they do not take intoconsideration the differences in data recording capabilities between onepair of head and recording surface, and another head and surface pair.Though the heads are designed to perform identically in read/writeoperations, in practice different heads in a disk drive can havedifferent read/write performance capabilities. Lower performing headscannot read/write data as that of other heads in the disk drive.Typically, a single error rate level and a single storage capacity levelare used to record data for all the pair heads and surfaces. Thisresults in inefficient data storage for those pairs of heads andsurfaces that can store more data. It also lowers the qualificationyields of the disk drives because one or more pairs of heads andsurfaces do not record data at the qualifying error rate and capacitylevels.

[0005] Further, in high data rate design of disk drives, as therecording density (i.e. bits-per-inch and/or tracks-per-inch) isincreased, maintaining transducer head tolerances has become achallenge. Variance in the relative head performance distributionincreases with increasing data density. In conventional disk drives, thedrive yield and capacity suffers as a result of head performancevariations in disk drives.

[0006] One method of increasing the data storage capacity of a diskdrive includes increasing the areal density of the data stored on themedia surfaces (bits/sq. in.—BPSI). Areal density is the track densitywhich is the number of tracks per radial inch (TPI) that can be packedonto the media/recording surface, multiplied by the linear density (BPI)which is the number of bits of data that can be stored per linear inch.

[0007] Conventional processes for qualifying disk drives scrap a diskdrive when the measured disk capacity of the disk drive is less than atarget disk capacity. Conventionally, each recording surface isformatted to store the same amount of data as every other recordingsurface. Thus, a recording surface that has a low error rate isformatted to the same TPI and BPI levels, as a recording surface havinga high error rate, even though it can store more data. However, byadopting a single TPI and BPI level for every recording surface,conventional processes fail to account for the differences insensitivity and accuracy of the paired head and recording surface, whichresults in less data storage and more waste of space on each recordingsurface. This also results in lower overall yields of disk drivesbecause if even a few of the recording surfaces do not meet theirtargeted capacity, the sum of the surface capacities of all the mediasurfaces will be less than the target capacity, causing the entire diskdrive to fail.

[0008] Some conventional disk drives utilize Variable Bits Per Inch tooptimize utilization of the linear density capabilities of the heads.However, with increasing TPI, it is difficult to control tolerance ofthe head width relative to the shrinking track pitch. As a result,either head yield and/or drive yield suffer.

[0009] There is, therefore, a need for a method of storing data in adisk drive which improves disk drive yield while meeting the desiredtarget drive capacity or increasing the drive capacity while meeting adesired drive yield by taking advantage of the head performancevariation.

BRIEF SUMMARY OF THE INVENTION

[0010] The present invention utilizes Vertical Zoning to improve theyield/performance of storage devices such as disk drives by optimizingthe TPI and optionally BPI of each head/media pair in the storagedevice. In one embodiment, the present invention provides a method ofimplementing Vertical Zoning which applies to disk drives with multipleheads. For single head disk drives, the same method of Vertical Zoningcan be used to trade off TPI against BPI to improve drive yield andperformance.

[0011] In one version, a method of defining storage format in a datastorage device having a plurality of storage media and a plurality ofcorresponding data transducer heads is provided, wherein each transduceris head for recording on and playback of information from acorresponding storage medium. A storage format is defined in at leastone region on each storage medium, wherein each region includes aplurality of concentric tracks for recording on and playback ofinformation. The method includes the steps of: moving each storagemedium with respect to the corresponding transducer head and readingdata from each storage medium with the corresponding transducer head;measuring a record/playback performance capability of each transducerhead; and selecting a group of track densities, one track density foreach region on a storage medium, based on the measured record/playbackperformance capability of the corresponding transducer head.

[0012] In another version, the TPI density is optimized across portionsof a single media surface. A TPI is selected and data is recorded on aportion of the media surface at the selected TPI. The level of trackdensity (TPI) can be one of fixed number of preselected levels or can bederived from an algorithm that is based on the location of a portion ofthe media surface. Thereafter, the recorded data is read and an errorrate of the recorded data is measured. The measured error rate iscompared to an acceptable error rate, and if the measured error rate isgreater than the maximum acceptable error rate, the previous steps arerepeated for another track density value, for example, the originallyselected value less a decrement. This process continues until themeasured error rate is less than or equal to the acceptable error rate,to provide a maximum recordable track density of data for a particularportion of the media surface.

[0013] Yet in another version, the present invention provides a datastorage device having a plurality of storage media and a plurality ofcorresponding data transducer heads, each transducer head for recordingon and playback of information from a corresponding storage media. Astorage format is defined in one or more regions on each storage media,wherein each region includes a plurality of concentric tracks forrecording on and playback of information, by steps including: measuringa record/playback performance capability of each transducer head; andselecting a group of track densities, one track density for each regionon each storage media, based on the measured record/playback performancecapability of the corresponding transducer head; wherein said multipleregions on each storage media are arranged as concentric regions, eachregion having an inner and an outer boundary at different radiallocations on the storage media, such that each storage media includesthe same number of concentric regions as other storage media in thatdata storage device, wherein the boundaries of radially similarlysituated regions on all the storage media in that data storage deviceare essentially at the same radial locations.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] These and other features, aspects and advantages of the presentinvention will become understood with reference to the followingdescription, appended claims and accompanying figures where:

[0015]FIG. 1 shows an example partial schematic diagram of a disk drivewith an example data storage format according to the present invention;

[0016]FIG. 2 shows another example schematic of the disk drive of FIG. 1illustrating disk drive electronics;

[0017]FIG. 3 shows an example surface format for data storage accordingto the present invention;

[0018]FIG. 4 shows an example flow chart of an embodiment of steps ofdefining a data storage surface format according to the presentinvention;

[0019]FIG. 5 shows an example flow char of an embodiment of determiningstorage capacity according to the present invention;

[0020]FIG. 6 shows a conventional data storage format;

[0021]FIG. 7 shows an example layout of data storage format for a diskdrive with multiple heads according to the present invention

[0022]FIG. 8 shows an example storage format including capacity zones;

[0023]FIG. 9 shows an example of variable servo track with variable datatrack data storage format layout;

[0024]FIG. 10 shows an expanded view for an example data storage layoutincluding fixed servo track pitch with variable data track pitch for azone on a disk surface;

[0025]FIG. 11 shows an example data storage layout including fixed servotrack vs. variable data track for 2-head disk drives;

[0026]FIG. 12 shows a conventional logical cylinder format LBA accessmodel for 4-head disk drives;

[0027]FIG. 13 shows an example virtual cylinder data storage surfaceformat LBA access model for 4-head disk drives according to the presentinvention;

[0028]FIG. 14 shows another example block diagram depicting logicalblock address accessing scheme according to an example surface formataccording to the present invention for a two head disk drive;

[0029]FIG. 15 shows another example block diagram depicting logicalblock address accessing scheme according to an example surface formataccording to the present invention for a four head disk drive;

[0030]FIG. 16 shows an example capacity zone for storage surface in diskdrives according to the present invention;

[0031]FIG. 17 shows an example flowchart of embodiment of steps ofoptimizing recording density per zone; and

[0032]FIG. 18 shows an example flowchart of embodiment of steps ofdetermining head performance.

DETAILED DESCRIPTION OF THE INVENTION

[0033] Data storage devices used to store data for computer systemsinclude, for example, hard disk drives, floppy disk drives, tape drives,optical and magneto-optical drives, and compact disk drives. Althoughthe present invention is illustrated by way of an exemplary magnetichard disk drive, the present invention can be used in other storagemedia and drives, including non-magnetic storage media, as apparent toone of ordinary skill in the art and without deviating from the scope ofthe present invention.

[0034] Referring to FIGS. 1-2, an exemplary hard disk drive 100 isdiagrammatically depicted for storing user data and/or operatinginstructions for a computer system 54. The hard disk drive 100 comprisesan electromechanical head-disk assembly 10 as including one or morerotating data storage disks 12 mounted in a stacked, spaced-apartrelationship upon a rotating spindle 13. The spindle 13 is rotated by aspindle motor 14 at a predetermined angular velocity.

[0035] Each disk 12 defines at least one media surface 23, and usuallytwo media surfaces 23 on opposing side of each disk 12. Each mediasurface 23 is coated with magnetic or other media for recording data.The spindle drive motor 14 turns the spindle 13 in order to move/rotatethe disks 12 past magnetic transducer heads 16 suspended by suspensionarms 17 over each media surface 23. Generally, each magnetic head 16 isattached to the suspension arm 17 by a head gimbal assembly (not shown)that enables magnetic head 16 to swivel to conform to the media surfaceson the disks 12. The suspension arms 17 extend radially from a rotaryvoice coil actuator (not shown). An actuator motor 20 rotates theactuator and head arms and thereby positions the magnetic heads 16 overthe appropriate areas of the media surfaces 23 in order to locate andread or write data from or to the storage surfaces 23. Because the disks12 rotate at relatively high speed, the magnetic heads 16 ride over themedia surface 23 on a cushion of air (air bearing). Each magnetic head16 comprises a read element (not shown) for reading magnetic data onmagnetic storage media surfaces 23 and a write element (not shown) forwriting data on the media surfaces 23. Most preferably, although notnecessarily, the write element is inductive and has an electricalwriting width which is wider than an electrical reading width of theread element, which is preferably of magnetoresistive or giantmagnetoresistive material.

[0036] Referring to FIG. 3, each media surface 23 is divided into aplurality of concentric circular tracks 30 that each have individuallyaddressable portions 35, such as sectors, in which data is stored in theform of magnetic bits. The data sectors 35 are separated by embeddednarrow servo sectors or spokes 25 which include a series ofphase-coherent digital fields followed by a series of constant frequencyservo bursts. The servo bursts are radially offset andcircumferrentially sequential, and are provided in sufficient numberssuch that fractional amplitude signals picked up by the read elementfrom portions of at least two bursts passing under the read elementenable the controller 57 (FIG. 2) to determine and maintain proper headposition relative to a data track 30. One example of a servo burstpattern for use with an inductive write element/magneto-resistive readelement head 16 is provided by commonly assigned U.S. Pat. No.5,587,850, entitled: “Data Track Pattern Including Embedded ServoSectors for Magneto-Resistive Read/Inductive Write Head Structure for aDisk Drive”, incorporated herein by reference.

[0037] The drive controller 57 controls operation of the pairs ofmagnetic heads 16 and media surfaces 23 to read and write data onto eachmedia surface 23. The drive controller 57 preferably comprises anapplication specific integrated circuits chip which is connected by aprinted circuit board 50 with other chips, such as a read/write channelchip 51, a motors drive chip 53, and a cache buffer chip 55, into anelectronic circuit as shown in FIG. 2. The controller 57 preferablyincludes an interface 59 which connects to the host computer 54 via aknown bus structure 52, such as ATA or SCSI.

[0038] The controller 57 executes embedded or system software comprisingprogramming code that monitors and operates the controller system anddriver 100. During a read or data retrieval operation, the computersystem 54 determines the “address” where the data is located on the diskdrive 100, i.e., magnetic head number, the track 30, and the relevantportion(s) 35 of the track 30. This data is transferred to the drivecontroller 57 which maps the address to the physical location in thedrive, and in response to reading the servo information in the servosectors 25, operates the actuator motor 54 and suspension arm 17 toposition a magnetic head 16 over the corresponding track 30. As themedia surface 23 rotates, the magnetic head 16 reads the servoinformation embedded in each spoke 25 and also reads an address of eachportion 35 in the track 30. When the identified portion 35 appears underthe magnetic head 16, the entire contents of the portion 35 containingthe desired data are read. In reading data from the media surface 23,the read element (not shown) senses a variation in an electrical currentflowing through a magnetoresistive sensor of the read element (notshown) when it passes over an area of flux reversal on the surface 23 ofthe media. The flux reversals are transformed into recovered data by theread/write channel chip 51 in accordance with a channel algorithm suchas partial response, maximum likelihood (PRML). The recovered data sthen read into the cache memory chip 55 of the disk drive 100 fromwhence it is transferred to the computer system 54. The read/writechannel 51 most preferably includes a quality monitor function whichenables measurement of the quality of recovered data and therebyprovides an indication of data error rate. One channel implementationwhich employs channel error metrics is described in commonly assignedU.S. Pat. No. 5,521,945 to Knudson, entitled: “Reduced Complexity EPR4Post-Processor for Sampled Data Detection”, incorporated herein byreference. The indication of recovered data error is used in order toselect linear data density, track density and/or error correction codelevels, in accordance with principles of the present invention, as morefully explained hereinbelow.

[0039] Writing or storing data on the media surface 23 is the reverse ofthe process for reading data. During a write operation, the hostcomputer system 54 remembers the addresses for each file on the mediasurface 23 and which portions 35 are available for new data. The drivecontroller 57 operates the actuator motor 54 in response to the servoinformation read back from the embedded servo sector 25 in order toposition a head 16, settles the head 16 into a writing position, andwaits for the appropriate portions 35 to rotate under the head 16 toperform the actual writing of data. To write data on the media surface23, an electrical current is passed through a write coil in theinductive write element (not shown) of the head 16 to create a magneticfield across a magnetic gap in a pair of write poles that magnetizes themagnetic storage media coating the media surface 23 under the head 16.When the track 30 is full, the drive controller 57 moves the magnetichead 16 to the next available track 30 with sufficient contiguous spacefor writing of data. If still more track capacity is required, anotherhead 16 is used to write data to a portion 35 of another track 30 onanother media surface 23.

[0040] In one aspect, the present invention increases the data storagecapacity and yield of data storage devices having a plurality of mediasurfaces 23, such as hard disk drive 100 including disks 12 covered withmagnetic media. In one method, shown by example in FIG. 4, TPI densityfor each portion 35 of a media surface 23 is individually selected bymeasurement to optimize the data storage capacity of that particularportion 35. Initially, values of TPI density are predefined and storedin a table of values that is input to a testing and formatting program.Generally, these values are incremental or decremental values of oneanother; for example, a maximum value or maxima of TPI density of datacan be the highest number in a series of five TPI density values. Thevalues of TPI density can be a fixed number of preselected levels or canbe derived from an algorithm that is based on a particular pair ofmagnetic head 16 and media surface. The TPI can be continuouslyvariable, depending on track radius or radial data tack zone. Inaddition, an acceptable error rate value, which represents the greatesterror rate than can be tolerated, is also input into the testing andformatting program.

[0041] In one version of the present invention, the TPI density isoptimized across portions 35 of a single media surface. As shown in FIG.4, a TPI is selected (step 85) and data is recorded on a portion of themedia surface 23 at the selected TPI (step 90). The level of trackdensity (TPI) can be one of fixed number of preselected levels or can bederived from an algorithm that is based on the location of a portion 35of the media surface 23. Thereafter, the recorded data is read (step101) and an error rate of the recorded data is measured (step 105). Themeasured error rate is compared to an acceptable error rate (step 110),and if the measured error rate is greater than the maximum acceptableerror rate, the previous steps are repeated for another track densityvalue, for example, the originally selected value less a decrement (step115). This process continues until the measured error rate is less thanor equal to the acceptable error rate, to provide a maximum recordabletrack density of data for a particular portion 35 of the media surface23.

[0042] Preferably, in the first iteration, the selected track density isa maximum value for the pair of magnetic head 16 and media surface 23(step 125). The maxima is calculated or estimated from statisticallycompiled data of measured track density for a population of pairs ofmagnetic heads 16 and media surface 23. It is preferred to start withthe maximum track density to provide the highest track density value ineach portion 35 of the media surface 23 in the fastest time, assumingthat the worst media surface 23 has a track density value closer to themaxima than the minima.

[0043] Because of a skew angle attributable to geometrical relationshipsbetween the surface 23 and the rotary actuator, track density values canbe increased radially from the innermost tracks 30 a (FIG. 3) near thecenter of a media surface 23 to the outermost tracks 30 b near itsperiphery. The outer tracks 30 b may have the same number of portions 35as the inner tracks 30 a, they can be made thinner in the radialdirection and more closely spaced, thereby providing higher data storagecapacities.

[0044] The track density can also be varied from one media surface 23 toanother media surface 23. Track density is increased by decreasingeither of the track width or the spacing between adjacent tracks 30.Preferably, the track density is varied by varying the spacing betweenadjacent tracks 30, because the width of the tracks 30 is determined by,and its variation limited to, the writing width or geometry of the writeelement of the magnetic head 16. The variation in track densities fromone media surface 23 to another can be customized, or selected from thenumber of preselected levels of track density.

[0045] In a preferred method of determining the maximum recordable trackdensity, the embedded servo sector 25 are initially written on a mediasurface 23 during a factory servo-writing process at a servo trackdensity that is higher than the data track density, as illustrated inFIG. 3. Servo bursts within each servo sector 35 are provided in suchnumber and placement to enable accurate positioning of the magnetic head16 in a full range of positions across the media surface 23. Given theparticular effective width and characteristics of the read element of aparticular head (the read element width typically being narrower thanthe writer) information in the embedded servo sector 25 is read by themagnetic head 16 and passed to the drive controller 57 which directs theactuator motor 20 to readjust the position the suspension arm 167. Thisis important because high track densities require highly accuratepositioning of the suspension arm 17, and the data track density cannotbe greater than the servo track density. Generally, as shown in FIG. 3example, the servo track density is about 150% of the maximum possibledata track density. In FIG. 3 five servo tracks Sa, Sb, Sc, Sd and Seare shown in relation to three data tracks Tk1, Tk2 and Tk3. Servo trackdensity is determined by determining the minimum read or write width ofa population of magnetic heads 16. After writing the servo wedges 25 atthe servo track pitch, the actual data track 30 can be written at anydisk radial position between the servo tracks, not just at null positionwhere equal amplitudes are observed from two different servo burstsreads from a servo wedge. Additional tests, as described above, areperformed to determine the optimum data track density of the mediasurface 23. Each servo track comprises radially similarly situated servoinformation in servo wedges 25 (e.g., the set of servo information Se atessentially same radial distance from the disk center form a servo trackcircumferrentially, set of servo information Se at essentially sameradial distance from the disk center form another servo trackcircumferrentially, etc.).

[0046] Most preferably, every disk drive is servo written at the factoryat a second track density (servo TPI) which is sufficiently high toprovide accurate positioning at any radius for the fill range ofacceptable read/wrote widths of the read and write elements of aparticular head 16. Data track density (data TPI) is then decoupled fromservo TPI by writing data tracks centered at non-null positions of theservo pattern. Micro-jig techniques are employed by the controller 57 inorder to carry out the desired positioning over the data tracklocations. Initial servo TPI is determined by determining an minimumread element width of an acceptable population of heads (as also bydetermining a maximum write width of the same acceptable population, ifuntrimmed servo bursts are employed in each servo sector 25). More servobursts an be provided to ensure adequate linearity of servo positionerror signal (PES) derived by reading relative burst amplitudes at anyparticular disk radius for a worst case read element and head.

[0047] While an example servo track density is presently approximately150% of the data TPI, the present invention provides increasing servoTPI relative to average data TPI to ensure that a read element on thenarrow end of the distribution has sufficient width of linear responseto provide a useable PES for use by the controller 57.

[0048] Following the factory servowriting process, additional timeduring drive self-scan is needed to determine the optimum data TPI foreach data surface 23. One preferred method, described further below, isto perform “747” measurements that can be used to determine the optimumtrack pitch (the expression “747” comes from a similarity in appearancebetween a resultant data plot and an elevational outline of the Boeingmodel 747 airplane). The head 16 is moved off track until the error rateexceeds as chosen threshold. The distance to failure is called off trackcapacity. This process is repeated with adjacent tracks written atsmaller spacing until the off track capability drops to zero. Theresulting data for off track capability versus track pitch can then beanalyzed to determine the optimum track pitch, typically chosen as thetrack pitch with maximum off track capability. This process is describedin more detail in an article by R. A. Jensen, J. Mortelmans, and R.Hauswitzer, entitled: “Demonstration of 500 Megabits per Square Inchwith Digital Magnetic Recording”, IEEE Trans. on Magnetics, Vol. 26, No.5, September 1990, p. 2169 et seq. However, a simple in-drive erasewidth measurement may also be used to determine suitable data TPI.

[0049] The optimized track density determined can also be used tooptimize the yield or “qualifying pass rate” of the data storagedevices. The example flowchart in FIG. 5, shows steps of animplementation of this process for increasing the yield and data storagecapacity of the disk drive 100 including the plurality of media surfaces23. In this method, in a determining step 150 maximum track density ofdata (optionally maximum recordable linear density of data) isdetermined for each media surface 23 using the methods described above.Optionally, the media surface 23 is formatted using the predeterminedmaxima of track density in a formatting step 152. Then, in a calculationstep 155 the surface capacity of each media surface 23 is calculatedfrom the measured, maximum recordable density. The surface capacity isdescribed by the equation: TPI×BPI×(1+ECC)/FE, wherein TPI is trackdensity, BPI is the linear density, ECC is the fractional level of errorcorrecting code used which is typically about 0.1, and FE is the formatefficiency which is typically about 0.57.

[0050] After each media surface 23 has been formatted, the calculatedsurface capacities of all formatted surfaces 23 are summed in a summingstep 160 to determine the device capacity, which is the storage capacityof the entire data storage device 100. If the device capacity equals orexceeds a target or desired storage capacity, the data storage device100 is passed, and it is not necessary to determine optimal TPI, BPI andECC levels for any more media surfaces 23. However, if the sum of thecapabilities of all measured surfaces does not equal or exceed thetarget capacity, it is determined if all surface 23 have been measured.If all the media surfaces 23 have not been measured, the surfacecapacity of the next media surface 23 is determined, and if the devicecapacity is still less than the target capacity, the disk drive 100 isfailed. After the disk drive 100 is qualified, testing ends, and thedrive controller 57 is programmed for the appropriate track density andlinear density for formatting each media surface 23. The drivecontroller 57 is also programmed to apply a measured or calculated levelof error code to each media surface 23 during formatting. The abovemethods are utilized to manufacture storage devices such as disk drives100, with storage media surface formats according to the methodsdescribed herein.

[0051] In every storage device such as the disk drive 100, there is adistribution associated with head/media pair performance in that diskdrive. In another aspect, the present invention takes advantage of thatdistribution to determine different/variable TPI assignment for heads,and optionally variable BPI.

[0052] As described, in conventional disk drives, the TPI is the samefor each head and corresponding disk surface, regardless of thecapabilities of different heads in the disk drive. Example FIG. 6 showsconventional layout in disk drives, wherein the TPI is the same for eachhead and corresponding disk surface, regardless of the capabilities ofdifferent heads in the disk drive. In the example of FIG. 6, the diskdrive includes N heads, with fixed servo track pitch and fixed datatrack pitch for each zone for heads 0, . . . , N−1. For all heads, thereare 45 servo tracks, wherein: Head 0: 15 Data Tracks 15 Data Tracks per45 Servo Tracks Head 1: 15 Data Tracks 15 Data Tracks per 45 ServoTracks . . . . . . Head N-1: 15 Data Tracks 15 Data Tracks per 45 ServoTracks

[0053] However, according to the present invention, for a desired diskdrive capacity, based on the number of heads/surfaces, a suitable TPI(and optionally BPI) per head-surface pair is selected to satisfy thedesired disk drive capacity. Based on the capability of head andcorresponding capacity of each disk surface, using variable TPI, a datastorage (surface) format per disk surface in the disk drive is thendetermined.

[0054] As such, for example, once a disk drive 100 with multiple heads16 is assembled, then each head's recording capability/performance isdetermined. Then if a head 16 is better performing, then the TPI forthat head is increased. And, if a head 16 is has lower performance, thenthe TPI for that head 16 is decreased. By making TPI per surface portionadjustable to the capability of the corresponding head 16, a higherperforming head compensates for a lower performing head, whereby thedisk drive capacity remains at the desired capacity. In another aspectof the present invention, variable TPI is utilized to optimize diskdrive capacity by providing an optimum TPI for each head 16 in the diskdrive 100 according to the capability of the head 16.

[0055] In one example, a higher performing head 16 can record atnarrower track pitch than a lower performing head 16. This allows forvariable TPI for different disk surfaces, by increasing the number oftracks per inch for the higher performing head, and decreasing thenumber of tracks per inch for the lower performing head. Overall, thedisk drive capacity remains at the desired value or is increased overconventional disk drives.

[0056] For variable TPI, each head's performance is determined duringtesting (e.g., determining TPI tolerance for each head). For a desireddisk drive capacity, an optimization process selects suitable TPI (andoptionally BPI) to each head based on that head's measured performance,to achieve (or surpass) the desired disk drive capacity. Theoptimization process is performed per head 16 per disk drive 100, andcan be performed during a self-scan of each disk drive 100.

[0057] The aforementioned methods according to the present invention aredescribed in further detail below.

[0058] Vertical Zoning

[0059] Referring to FIG. 7, an example track layout in a disk drive withn heads is shown. Each disk surface 23 is divided into severalconcentric zones 27 for writing data to and reading data from using acorresponding head 16, wherein each zone 27 includes multiple datatracks 30. Example FIG. 16, described further below, shows anotherexample of several capacity zones 27 for a disk drive surface 23.

[0060] Referring to FIG. 8, according to an embodiment of the presentinvention, each zone 27 includes a number of concentric virtualcylinders (sub-zones or regions) 29, wherein each virtual cylinder (VC)29 includes a number of data tracks 30 between radially spacedboundaries for each VC 29. The disk drive includes concentric VCs fromID to OD on all disk surfaces. There are multiple zones 27 per disksurface 23, and there are multiple VCs 29 (e.g., VC0 . . . VCn) per zone27. Within a VC 29 there are multiple servo and data tracks. Further, asshown in FIG. 1, each VC 29 (e.g., VC1 . . . VCM, . . . , etc.) extendsvertically between a first surface 23 of a first disk 12 (e.g., Disk1)and a second surface 23 of the last disk 12 (DiskN) in the disk stack inthe disk drive 100.

[0061] Conventionally there is a fixed number of data and servo trackson disk surfaces, and there is a fixed ratio of data tracks relative toservo tracks in a zone from one surface to the next. However, accordingto the present invention, in each VC 29, the density of data tracks 30(TPI) can change from surface 23 to surface 23, the number of servotracks (e.g., servo tracks per inch) can change from surface 23 tosurface 23, and the ratio of the number of data tracks to the number ofservo tracks can change from surface 23 to surface 23. Further, on eachdisk surface 23, the number of data tracks (TPI) can change from VC 29to VC 29, the number of servo tracks (e.g., servo tracks per inch) canchange from VC 29 to VC 29, and the ratio of the number of data tracksto the number of servo tracks can change from VC 29 to VC 29.

[0062] For example, the ratio of data tracks relative to servo tracks ina VC 29 can change from one surface 23 to the next. In another example,each VC 29 may include the same number of servo tracks from one surfaceto the next, but may have different number of data tracks from onesurface to the next in the same VC 29. On the same disk surface, therecan be the same number of servo tracks from VC 29 to another, but theremay be different number of data tracks from one VC 29 to another.

[0063] In one embodiment the present invention provides a method(Vertical Zoning) to provide different area track densities/formats ondifferent disk surfaces 23 in relation to corresponding heads 16, tomatch those area densities optimally with the capabilities of each head16. In Vertical Zoning, the area density is obtained by varying thetrack density TPI (and optionally BPI) in relation to the heads. Assuch, a weak head 16 which does not meet the requirement for a selectedTPI (and optionally BPI), is assigned to a lower TPI (and optionallyBPI), and is compensated by strong head(s) which are capable of morethan the selected TPI, by adapting TPI (and optionally BPI) per headsuch that the same disk drive capacity is maintained.

[0064] Variable TPI

[0065] In one version of the present invention, variable TPI is used toimplement Vertical Zoning. In order to provide variable TPI, a surfaceformat (i.e., virtual cylinder format) is utilized instead ofconventional cylinder format (FIG. 6) for logical block addressing. Withthat surface format, variable TPI is supported across different datazones 27 and across different disk surfaces 23.

[0066] Examples of variable TPI implementations according to the presentinvention, are now described.

[0067] In one example, variable TPI is implemented by varying the servotrack pitch profile for each head 16 during servo-writing process.Example FIG. 9 shows ratio of data tracks 30 to servo tracks 31,providing variable number of servo tracks 31 with fixed number of datatracks 30, per head 16. As such, Head 0 and Head 1 have different ratioof number of data tracks 30 per number of servo tracks 31.

[0068] In another example, the number of servo tracks 31 perhead-surface pair changes, while the ratio of data tracks 30 to servotracks 31 remains the same for all surfaces 23 (e.g. 3 servo tracks foreach 2 data tracks). Using a fixed ratio between servo tracks 31 anddata tracks 30, by increasing/decreasing the number of servo tracks 31,the number of data tracks 30 automatically increase/decrease, and sodoes the surface capacity. Based on each head's performance, thecorresponding disk surface 23 may have a different number of servotracks 31 (and data tracks 30) than other disk surfaces 23.

[0069] In another example, variable TPI is implemented by maintainingthe same servo track pitch profile for all heads/surfaces, and varyingthe data track pitch relative to the servo track pitch withoutservo-writing each surface at a different servo track pitch profile.

[0070]FIG. 10 shows an expanded view for an example fixed servo trackpitch with variable data track pitch for a zone 27 (e.g., Zone1),wherein for all heads 16 there are 45 servo tracks 31, such that: Head0: 15 Data Tracks 15 Data Tracks per 45 Servo Tracks Head 1: 18 DataTracks 18 Data Tracks per 45 Servo Tracks . . . . . . Head N: 12 DataTracks 12 Data Tracks per 45 Servo Tracks

[0071]FIG. 11 shows example details of servo track 31 and data track 30ratio for fixed servo track pitch with variable data track pitch. Assuch, in VC0 there are fixed servo tracks 31 for a 2 head model withvariable data tracks 30 (e.g., for Head0 and Head1, there are the samenumber of servo tracks 31, but data tracks 30 vary for Head0 and Head1).The same format is provided for VC1, wherein the data track densitychanges and the servo track density remains fixed. The servo tracks 31for all heads are written the same way, however based on each head'srecord/playback performance, in self-scan process for putting down datatracks 30, for one head e.g. 3 servo tracks 31 for every 2 data tracks30 are used, and for another head the ratio is changed to 3 servo tracks31 for every 2.2 data tracks 30. Therefore, data tracks 30 can be eithercloser to each other, or further apart, depending on how the data trackto servo track ratio is changed. As such, in this case the data tracks30 are no longer physically aligned vertically in cylinders. And, forlogical block sequencing, instead of a conventional cylinder format(FIG. 12), the surface format (i.e., virtual cylinder) is utilized.

[0072] As shown in FIGS. 6 and 12, in conventional disk drives the datatracks are organized into concentric data zones. With multipletransducer heads in a disk drive (e.g., one head per disk surface), thedata zones are aligned vertically. Within each data zone, the same TPIis used for all the heads on different disk surfaces. The data tracks ondifferent disk surfaces are aligned vertically, forming logicalcylinders in which logical data blocks are accessed sequentially. Whenaccessing data sequentially within logical a cylinder, a head switch isperformed between consecutive data tracks. At the last head, a singletrack seek is performed to read data from the next logical cylinder. Inthis description, data track pitch indicates distance between twoadjacent data tracks 30, and servo track pitch indicates distancebetween two adjacent servo tracks 31.

[0073] As shown in FIG. 12, in conventional disk drives wherein datatracks on different disk surfaces lineup vertically in cylinders, toaccess data logically, every time reading data from a logical cylinderon one disk surface is complete a head switch is performed to anotherdisk surface to continue logical data access. For example, in a 4-head,2-disk, disk drive, as data is accessed in a logical cylinder going downvertically from e.g. head0−surface0 on the first disk to head3−surface3on the second disk, after accessing data on a track on surface0 usinghead0, a switch to head1 of surface1 is performed and data is read froma track in the same logical cylinder from surface1. This processcontinues (e.g., head2−surface 2, head3−surface 3) until all data inthat logical cylinder is accessed. Then a seek is performed to the nextlogical cylinder, and data read that from that next logical cylinder ina similar fashion described above.

[0074] However, referring to example FIG. 13, for disk drives withvariable TPI according to the present invention, the conventionalcylinder format for logical block addressing is undesirable because ofperformance degradation caused by a head switch which may also involve atrack seek. Instead, the surface format according to the presentinvention for logical block addressing improves the drive performance,and TPI can vary from virtual cylinder 29 to virtual cylinder 29, zone27 to zone 27 and from surface 23 to surface 23. With the examplevariable TPI format according to the present invention, the data tracks30 on different disk surfaces 23 may no longer align vertically. Toreduce the head switch time and to improve the drive's performanceduring logical operations, it is preferable to utilize the surface dataformat according to the present invention instead of the conventionallogical cylinder format. With the surface format, all disk surfaces aredivided into said virtual cylinders 29. The virtual cylinders 29 aredefined in relation to servo tracks 31 and are aligned vertically fromone disk surface 23 to the next. However, within the same virtualcylinder 29, the corresponding data track density (TPI) can be differenton different surfaces.

[0075] As shown in the example FIG. 13, when sequentially accessinglogical blocks according to the present invention, a single track seekis used instead of head switch within the same virtual cylinder 29 forspeed. At the end of a virtual cylinder 29, a head switch occurs andsequential access continues on the surface 23 of another (e.g., next)disk in the opposite direction. In FIG. 13, when all tracks 30 in a VC29 on one surface (e.g., Surface0−Head0) are read, a head switch to thenext surface (Surface1−Head1) in the same VC 29 is performed to read thetracks 30 therein, until all tracks on all surfaces for that VC 29 areread (or written). FIG. 13 shows example track access in one VC 29.

[0076] In another example, head switch from Head0 to Head1 can bedirect, wherein e.g., in FIG. 13 reading data started top of first block(VC1 on Surface0), zig-zag down the first block, then across to thesecond block (VC1 on Surface1) zig-zag up from the bottom of secondblock to the top of the second block, then across to the top of thethird block (VC1 on Surface2) zig-zag down to the bottom of the thirdblock, etc. FIGS. 14 and 15 show other example block diagrams depictingthe logical block address accessing scheme using the above examplesurface format for two-head disk drives and four-head disk drives,respectively. In example FIG. 14, an example logical block addressing(LBA) scheme for two-head, 2 surface, disk drives is shown. For the samevirtual cylinder, the data is accessed by Head0 sequentially from Track0through Track12 on Surface0, then by Head1 from Track0 to Track6 onSurface1, then by Head0 from Track13 through Track25 on Surface0, thenby Head1 from Track7 through Track13 on Surface2, etc. In this example,Surface0 has higher TPI density than Surface1 in the same virtualcylinder. In example FIG. 15, another example logical block addressing(LBA) scheme for four-head, 4 surface, disk drives is shown.Sequentially, Head0 reads tracks in a VC 29 on Surface0, Head1 readstracks in that VC on Surface1, Head2 reads tracks in that VC onSurface2, Head3 reads tracks in that VC on Surface3, Head0 reads tracksin that VC on Surface0, Head1 reads tracks in that VC on Surface1, Head2reads tracks in that VC on Surface2, Head3 reads tracks in that VC onSurface3, etc. The surfaces can have different TPIs for the same VC 29.For illustration purposes, in the example of FIG. 11, for the two-headdisk drive, Head0 for one disk surface 23 supports 6 data tracks 30 fora virtual cylinder VC0, whereas Head1 for another disk surface 23supports 5 data tracks 30 for that virtual cylinder VC0.

[0077] Variable Data Track Pitch for Variable TPI Implementation

[0078] As aforementioned, one example variable TPI surface format isimplemented by varying the servo track pitch, wherein each disk surfacecan be servo written with a different servo track pitch profile. ExampleFIG. 9 shows 2 head format having different servo track pitch withdifferent data track pitch. To reduce the complexity of servo writingand to write the servo pattern in a single pass, in an alternativeexample method the servo track pitch profile remains constant in allsurfaces, and the variable TPI is implemented by varying the data trackpitch relative to the servo track pitch. By disassociating data tracksfrom a fixed ratio to the servo tracks, TPI can be determined aftersurfaces have been servo written. Example FIG. 11 shows a 2 head formathaving fixed servo tracks and variable data tracks.

[0079] In disk drives with MR-type heads, the servo system can read fromany track location depending on the offset between the writer and thereader elements of the heads. However, during writing, the servotypically writes at track center which is a spot with good TMR. Toimplement variable TPI with varying data track pitch, the servo systemmust be capable of writing at any desired track location, away from thetrack center, in locations with less than optimum TMR.

[0080] In one example, the number of data tracks 30 per virtual cylinder29 also varies from data zone 27 to data zone 27 across the stroke on adisk surface 23. Each data zone 27 can include a fixed number of virtualcylinders 29 for all heads 16. The number of virtual cylinders 29 is thesame across different disk surfaces 23 in the disk drive. In thisfashion, the surface format with virtual cylinder structure according toan embodiment of the present invention supports variable TPI across thezones and across the disk surfaces. An optimization technique todetermine the TPI (and optionally BPI) for each head according to thepresent invention is provided further below.

[0081] Other example formats according to the present invention includeVariable Zone Layout (Vertical Data Zoning) and Vertical Track Zoning.In Variable Zone Layout, areal density variation is implemented byvariable recording frequency (BPI) for each head 16 per disk surface 23.In Vertical Track Zoning (i.e., Vertical Zoning with variable TPI), theareal density variation is implemented by variable TPI for each head 16per disk surface 23.

[0082] In another example according to the present invention, variableBPI and variable TPI are combined to allow each head to be adapted suchthat the areal density capability of each head is better utilized byallowing the selection of both linear and track densities. With both TPIand BPI as variables, a single head disk drive can also be optimized bytrading off TPI against BPI. As such, areal density variation isimplemented by both variable TPI and variable BPI for each head per disksurface. In addition, the TPI and BPI can be adaptive across theactuator stroke. In that case, by dividing the disk surface 23 intocapacity zones 27 (e.g., FIG. 16) and by calculating capacity inreal-time during the self-scan test, the drive capacity can be optimizedacross the capacity zones depending on the head/media performance.During the self-scan test process, capacity optimization is performedbefore variable TPI/BPI optimization.

[0083] Optimization Process

[0084] The present invention also provides variable TPI (and optionallyvariable BPI) optimization process, wherein in one embodiment, anexample optimization process based on a 747 geometric model measurementis utilized. An example method 747 measurement is described in apublication titled “Measure a Disk-Drive's Read Channel Signals”, August1999, Test & Measurement World, Published by Cahners BusinessInformation, Newton, Mass.

[0085] This optimization process allows optimization of TPI (andoptionally BPI at the same time) during the self-scan test of the diskdrive to meet Off-track Capacity (OTC) performance and drive capacityrequirements. Further, the disk drive capacity can be maximized for agiven OTC performance. The optimization process can be applied to diskdrives with multiple heads and single head drives, wherein a drive witha single head can be optimized by trading off TPI against BPI.

[0086] In the following description, these terminologies are utilized.Capacity zone is the drive capacity of a zone (each disk surface isdivided into many zones). Linear density is the number of bits recordedper inch (BPI). Track Mis-Registration (TMR) indicates allowableposition error. Track density is the number of tracks per unit lengthsuch as inch which is measured in a direction perpendicular to thedirection in which the tracks are read (TPI). UOTC is UnsqueezedOfftrack Capacity. SOTC is Squeezed Offtrack Capacity.

[0087] Capacity Optimization Across Capacity Zones

[0088] In this example (Vertical Zoning Recording) TPI (and optionallyBPI) are adaptive depending on the head/media pair performance. Withvariable TPI, each disk surface 23 can be divided into multiple TPIzones or virtual cylinders 29 (e.g., FIG. 11), wherein each TPI zone 29overlaps multiple data zones. In addition, all disk surface(s) can befurther divided into multiple capacity zones 27 with each capacity zoneincluding multiple TPI zones 29. The capacity of each capacity zone 27is adaptive and is determined by the head/media performance at thecapacity zone 27. The formation of the capacity zones 27 allows thedrive capacity to be traded off between the capacity zones 27 whilestill maintaining the required drive capacity. The capacity optimizationis performed at nominal TPI/BPI before variable TPI/BPI optimization isperformed within each capacity zone.

[0089] Variable TPI/BPI Optimization

[0090] In an example variable TPI/BPI optimization, an algorithm basedon 747 geometric model is utilized. This algorithm allows optimizationof TPI and BPI at the same time during the self scan test of the driveto meet the OTC performance, and the drive capacity, requirements. Thedisk drive capacity for a given OTC performance can also be maximized.The algorithm can be applied to drives with multiple heads and diskdrives with only one head drive, wherein a drive with a single head canbe optimized by trading off TPI against BPI.

[0091] In order to use variable recording density (e.g., TPI), anexample technique according to the present invention includes the stepsof selecting and using TPI optimally on each disk surface correspondingto each head. The selection process is performed with variable TPIoptimization at self-scan test of the disk drive. Within each capacityzone, each head is assigned a TPI, optimally based on the OfftrackCapacity (OTC) performance of the heads within the capacity zone. For asingle head drive, this technique also allows the TPI to be traded offagainst BPI to obtain optimal capacity.

[0092] 747 curves are used to determine performance of the heads as afunction of head geometry. A 747 measurement of each head in the driveis obtained, to determine the proper TPI and optionally BPI for a headat each zone. The 747 measurements for each head can be taken atdifferent areas of a corresponding surface (e.g., inner, middle, outerdiameter, etc.). Therefore, in manufacturing during a test process,measurement of 747 performance of each head is obtained, and from the747 curves the TPI and BPI are selected to provide desired capacityformat for each head per zone and virtual cylinder. This is performedfor each head, and every surface in each disk drive. As such, in anexample, five disk drives with four heads each, meet a certain minimumcapacity (though disk drives need not have identical capacity), but eachdisk drive has a different surface format than others. This is becausesurface format optimization is performed for each head based on measuredperformance of each head/surface.

[0093] Referring to FIG. 17, in each disk drive, the record/playbackcapability of each head is determined (step 170). Then, the heads areranked according to capability (e.g., weak or strong) (step 172). Then asurface format such as TPI per head and zone (or virtual cylinder) isselected for each head in the disk drive (step 174). In one case, thereare several predetermined TPI formats, such as one for strong heads andone for weak heads. Ranking of the heads can have different levels, anda corresponding predetermined format for each level. As such, in anotherexample, the heads can be ranked weak, medium and strong, wherein apredetermine format is selected for each head. The total capacity iscalculated based on the selected formats for the heads (step 176), todetermine if required capacity and performance are satisfied for eachdisk drive (step 178). If not, TPI is traded off between the heads bychanging TPI of the heads until the desired capacity and performance(e.g., error rate) are satisfied (step 180). For example, stronger headsare assigned higher TPIs to increase capacity, and a weaker head areassigned lower TPI to meet error rate requirements.

[0094] Referring to FIG. 18, an example of the step 172 of determiningrecord/playback capability of each head includes the steps of: selectingTPI level per zone (step 190) and data is recorded with the head perzone on the media surface 23 at the selected TPI per zone (step 192).The level of track density (TPI) can be one of fixed number ofpreselected levels or can be derived from an algorithm that is based onthe location of a portion 35 of the media surface 23. Thereafter, therecorded data is read (step 194) and an error rate of the recorded datais measured (step 196). The measured error rate is compared to anacceptable error rate for each zone (step 198), and if the measurederror rate is greater than the maximum acceptable error rate for a zone,the previous steps are repeated for those zones another track densityvalue, for example, the originally selected value less a decrement (step200). This process continues until the measured error rate is less thanor equal to the acceptable error rate, to provide a maximum recordabletrack density of data for each head per zone (step 202) in the diskdrive 100. Preferably, in the first iteration, the selected trackdensity is a maximum value for the pair of magnetic head 16 and mediasurface 23.

[0095] In an example 747 measurement, a nominal BPI value is first usedto determine record/playback performance/capability of each head, andthen the assigned BPI for each head is adjusted based on head capabilityUsing a geometric 747 model, the performance of a head can be estimatedor measured with a 747 profile. Two points on the 747 profile at a fixederror rate, Unsqueezed Offtrack Capacity (UOTC) and Squeezed OfftrackCapacity (SOTC), can be used to uniquely define the 747 profileperformance of the heads. The purpose of the optimization in the diskdrive is to allow all the heads to have maximum UOTC and SOTC margins(i.e., Highest Offtrack Capability with a maximum disk drive capacity)while meeting the disk drive capacity and performance requirements. Thiscan be achieved by first moving the 747 curve of each head individually(i.e., by changing BPI and/or TPI), to a point of minimum performancemargin. A minimum performance margin point is defined by the minimumrequired SOTC at a pre-defined track squeeze. At this minimumperformance point, the disk drive is also at the maximum capacity point.The next step is to trade off capacity for more performance margin bymoving 747 curves of all the heads collectively (i.e., by changing BPIand/or TPI), to a point that meets the minimum capacity requirement. Bymoving the 747 curves of all the heads collectively, the same SOTCperformance margin is maintained. An example 747 geometric model and thevariable TPI/BPI technique are described in more detail below.

[0096] 747 Geometric Model

[0097] The use of SOTC and UOTC as performance metrics is based on anexample geometric 747 model. The UOTC and SOTC can be defined as afunction of write width (WW), read width (RW), erase width (E), trackpitch (TP), amount of squeeze (SQZ) and on-track bit error rate (BER) asshown in equations (1) and (2) below:

UOTC=(WW−RW)/2+E+f(BER)  (1)

SOTC=TP−SQZ−(WW+RW)/2+f(BER)  (2)

[0098] For BPI optimization, UOTC is used as the performance metric. Forany given head, WW, RW and E are all constant. Therefore, UOTC isdirectly a function of BER or BPI as shown in equation (3) below. Inaddition, SOTC is also a function of BPI if TP and SQZ are constant asshown in equation (4) below:

UOTC=f(BER)+C

BER=f(BPI), wherein C=constant

[0099] Whereby,

UOTC=f(BPI)+C  (3)

SOTC=TP−SQZ+f(BER)+C

SOTC=f(BPI)+C  (4)

[0100] For TPI optimization, SOTC is used as the performance metric. Fora given BPI, SOTC is a function of TP and SQZ. Therefore, the trackpitch or TP can be determined from the parameter SOTC once SQZ isdefined according to equations (5) and (6) below:

SOTC=TP−SQZ+C  (5)

TP=SOTC+SQZ−C  (6)

[0101] Variable TPI/BPI Optimization Algorithm

[0102] Prior to Variable TPI/BPI (vTPI/BPI) optimization, all the headsassume the nominal TPI/BPI and capacity, and each head can be positionedon a 747 profile according to its OTC capabilities. In one example, thefinal goal of the optimization is such that all the heads have similarUOTC and SOTC capabilities while meeting the overall drive capacityrequirement. This can be achieved by first moving the heads (i.e.,moving 747 curves of the heads by changing BPI and/or TPI) individuallyto a point of the minimum performance margin, and then moving 747 curvesof the heads collectively to meet the capacity requirement.

[0103] The optimization algorithm can be divided into two major parts.First, move the 747 profile (curves) of the heads individually to theminimum performance margin point defined by the drive requirements ofUOTC, SOTC, and SQZ. The point of minimum performance margin on allheads is also the point of maximum capacity for the drive. The drivecapacity is determined, and if the drive does not meet the minimumcapacity requirement at this point, the drive is either set back to thedefault condition or a best estimate is used to meet the capacityrequirement. Second, for the point of minimum performance and maximumcapacity, if the drive has excess capacity, the TPI and/or BPI for theheads can be relaxed by moving to a 747 profile with higher OTC marginto meet the capacity requirement. If the drive has less than therequired capacity, the TPI and/or BPI for the heads can be increased, bymoving to a 747 profile with lower OTC margin to meet the capacityrequirement. By adjusting all the heads by the same amount, the samemargin can be gained by all the heads, satisfying the requirement ofmaximizing the performance of the drive.

[0104] The basic steps of the example vTPI/BPI optimization processaccording to the present invention are listed below. The minimumperformance point is defined by the following test limits: UOTC1:minimum required UOTC + margin SOTC1: minimum required SOTC at SQZ1SQZ1: SQZ test point for SOTC1

[0105] The example optimization process includes the steps of:

[0106] 1. Find the minimum acceptable performance point for each head byfirst optimizing BPI: (a) run channel optimization for new BPI (forevery different data rate, there is channel optimization) and (b)optimize BPI within the allowed range of formats or data rates, suchthat the difference (UOTC−UOTC1) is minimized while satisfying therequirement of UOTC1<=UOTC.

[0107] 2. Find the minimum acceptable performance point for each head byoptimizing TPI: optimize track pitch within an allowed ATP (AdjacentTrack Pitch) range such that difference (SOTC−SOTC1) is minimized whilesatisfying the minimum performance requirement of SOTC1<=SOTC.

[0108] 3. Optimize BPIs for all the heads to meet the capacityrequirement: (a) calculate:delta_capacity=(current_capacity−minimum_capacity), and (b) ifdelta_capacity< >n*BPl_step_size, then increase/decrease BPI by n*x %,within the allowed BPI formats for each of the heads if possible.

[0109] 4. Optimize TPIs for all heads to meet the capacity requirement:(a) calculate the new capacity, determine the new delta_capacity, (b)calculate the delta_ATP allowed for each head, and ifdelta_capacity< >n*ATP_step_size, decrease/increase track pitch bydelta_ATP within the allowed ATP range for each of the heads ifpossible.

[0110] A data storage format and storage device according to the presentinvention provides many advantages over conventional disk drives.Because not all heads in disk drives perform the same way, inconventional disk drives, if one of multiple heads has a weakperformance and therefore can read/write at lower than expected storagecapacity, the overall disk drive capacity is lower than expected and thedisk drive is wastefully discarded as a failed drive. However, accordingto an embodiment of the present invention, by making the storage densityadaptable to the head capability, the storage format for a betterperforming head is adjusted such that the better performing head cancompensate for the weak head, and achieve the expected disk drivestorage capacity. This improves the disk drive yield and disk driveperformance, and reduces overall disk drive costs by allowing use ofdisk drives with weak heads. Further, by making the storage densityadaptable to the head capability, the storage format can be adjusted toobtain maximum capacity per disk drive depending on the performance ofthe heads in each disk drive.

[0111] The present invention has been described in considerable detailwith reference to certain preferred versions thereof; however, otherversions are possible. Therefore, the spirit and scope of the appendedclaims should not be limited to the description of the preferredversions contained herein.

What is claimed is:
 1. In a data storage device having a plurality ofstorage media and a plurality of corresponding data transducer heads,each transducer head for recording on and playback of information from acorresponding storage media, a method of defining storage format in oneor more regions on each storage media, wherein each region includes aplurality of concentric tracks for recording on and playback ofinformation, the method comprising the steps of: (a) moving each storagemedia with respect to the corresponding transducer head and reading datafrom each storage media with the corresponding transducer head; (b)measuring a record/playback performance capability of each transducerhead; and (c) selecting a group of track densities, one track densityfor each region on a storage media, based on the measuredrecord/playback performance capability of the corresponding transducerhead.
 2. The method of claim 1, further comprising the steps of: (d)defining the boundaries of each region based on the track densityselected for that region.
 3. The method of claim 1, wherein each trackdensity represents track pitch on a storage media.
 4. The method ofclaim 1, wherein: each storage media includes multiple regions, and step(c) further includes the steps of selecting a group of track densitiesfor each storage media, one track density for each region on thatstorage media, based on the measured record/playback performancecapability of the corresponding transducer head for that storage media.5. The method of claim 4, wherein: said multiple regions on each storagemedia are arranged as concentric regions, each region having an innerand an outer boundary at different radial locations on the storagemedia, step (c) further includes the steps of, for each storage mediaselecting a group of track densities, one track density for each regionon that storage media based on the measured record/playback performancecapability of the corresponding transducer head for regions on thatstorage media.
 6. The method of claim 5, further comprising the stepsof, before step (a), writing servo information in servo tracks at trackdensities on each storage media.
 7. The method of claim 6, wherein eachdata track density represents a data track pitch, and each servo trackdensity represents a servo track pitch relative to the data track pitch.8. The method of claim 7, wherein the data track pitch in two or moreregions on a storage media are different.
 9. The method of claim 7,wherein the servo track pitch in two or more regions on a storage mediaare different.
 10. The method of claim 7, wherein: the data track pitchin two or more regions on a storage media are different, and the servotrack pitch in said or more regions on that storage media are different.11. The method of claim 7, wherein: the data track pitch in two or moreregions on a storage media are essentially the same, and the servo trackpitch in said two or more regions on that storage media are different.12. The method of claim 7, wherein: the data track pitch in two or moreregions on a storage media are different, and the servo track pitch insaid two or more regions on that storage media are essentially the same.13. The method of claim 7, wherein: the ratio of data track pitch toservo track pitch in two or more of the regions on a storage media aredifferent.
 14. The method of claim 7, wherein: the ratio of data trackpitch to servo track pitch in two or more of the regions on a storagemedia are essentially the same.
 15. The method of claim 5, wherein eachstorage media includes the same number of concentric regions as otherstorage media in that data storage device, wherein the boundaries ofradially similarly situated regions on all the storage media in thatdata storage device are at the same radial locations.
 16. The method ofclaim 1, wherein in step (b) the steps of measuring is performed at oneor more locations on each storage media.
 17. The method of claim 1,wherein in step (b) each head performance is measured at one or moreread/write frequencies.
 18. The method of claim 1, wherein in step (b)each head performance is measured at one or more track densities. 19.The method of claim 1, wherein step (c) further includes the steps ofselecting said group of track densities to provide a required datastorage capacity for the data storage device.
 20. The method of claim 1,wherein step (c) further includes the steps of selecting said group oftrack densities to provides optimum data storage capacity for the datastorage device.
 21. The method of claim 1, wherein step (c) furthercomprises the steps of selecting said track densities, one track densityfor each region on a storage media based on the measured record/playbackperformance capability of the corresponding transducer head, to satisfya required storage capacity and performance for the data storage device.22. The method of claim 1, wherein step (c) further comprising the stepsof selecting a group of read/write frequencies, one frequency for eachregion, based on the measured record/playback performance capability ofthe corresponding transducer head.
 23. The method of claim 1, wherein instep (c) selecting said group of track densities further includes thesteps of selecting said group of track densities to satisfy a specifiedconstraint.
 24. The method of claim 23, wherein step (c) furtherincludes the steps of: (i) selecting a performance metric for each headin the data storage device; (ii) determining a performance capability ofeach head at different track densities per region; such that the stepsof selecting said group of frequencies further includes the steps of:(iii) ranking the performance capability values of all the headsdetermined in step (ii) with respect to said performance metric, if theperformance capability of at least one of said heads is below saidperformance metric and the performance capability of at least another ofsaid heads is above said performance metric, then reducing the trackdensity for the head having a performance capability below saidperformance metric by an amount sufficient to cause said head to performat least to the performance metric, and increasing the track density ofsaid at least another head, to satisfy said constraint.
 25. The methodof claim 24, wherein said constraint comprises providing at least arequired data storage capacity.
 26. The method of claim 24, wherein saidconstraint comprises providing at least a required storage deviceperformance.
 27. The method of claim 24, wherein said constraintcomprises providing at least a required data storage capacity andrequired storage device performance.
 28. The method of claim 1, whereinthe storage device comprises a disk drive and each storage mediacomprises a data disk.
 29. A data storage device prepared for storage ofdata by the method of claim
 1. 30. In a data storage device having aplurality of storage media and a plurality of corresponding datatransducer heads, each transducer head for recording on and playback ofinformation from a corresponding storage media, a method of definingstorage format in one or more regions on each storage media, whereineach region includes a plurality of concentric tracks for recording onand playback of information, the method comprising the steps of: (a)moving each storage media with respect to the corresponding transducerhead and reading data from each storage media with the correspondingtransducer head; (b) measuring a record/playback performance capabilityof each transducer head; and (c) selecting a group of track densities,one track density for each region on each storage media, based on themeasured record/playback performance capability of the correspondingtransducer head; wherein said multiple regions on each storage media arearranged as concentric regions, each region having an inner and an outerboundary at different radial locations on the storage media, such thateach storage media includes the same number of concentric regions asother storage media in that data storage device, wherein the boundariesof radially similarly situated regions on all the storage media in thatdata storage device are essentially at the same radial locations. 31.The method of claim 30, wherein step (c) further includes the steps of:for each set of radially similarly situated regions in the storagedevice, selecting a group of track densities, one track density for eachsaid region, based on the measured record/playback performancecapability of the corresponding transducer head for that region.
 32. Themethod of claim 31, further comprising the steps of, before step (a),writing servo information in servo tracks at track densities on eachstorage media.
 33. The method of claim 32, wherein each data trackdensity represents a data track pitch, and each servo track densityrepresents a servo track pitch relative to the data track pitch.
 34. Themethod of claim 33, wherein the data track pitch in two or more radiallysimilarly situated regions on two or more storage media are different.35. The method of claim 33, wherein the servo track pitch in two or moreradially similarly situated regions on two or more storage media aredifferent.
 36. The method of claim 33, wherein: the data track pitch intwo or more radially similarly situated regions on two or more storagemedia are different, and the servo track pitch in said or more regionsare different.
 37. The method of claim 33, wherein: the data track pitchin two or more radially similarly situated regions on two or morestorage media are essentially the same, and the servo track pitch insaid two or more regions are different.
 38. The method of claim 33,wherein: the data track pitch in two or more radially similarly situatedregions on two or more storage media are different, and the servo trackpitch in said two or more regions are essentially the same.
 39. Themethod claim 33, wherein: the ratio of data track pitch to servo trackpitch in two or more radially similarly situated regions on two or morestorage media are different.
 40. The method claim 33, wherein: the ratioof data track pitch to servo track pitch in two or more radiallysimilarly situated regions on two or more storage media are essentiallythe same.
 41. The method of claim 30, further including the steps of:(d) accessing data tracks in a set of radially similarly situatedregions by accessing data tracks in a first of said regions on a surfacevia a corresponding head, before accessing data tracks in a subsequentregion of said regions on another surface via a corresponding head. 42.The method of claim 30, further including the steps of: (d) accessingdata tracks in a set of radially similarly situated regions by, for eachof said regions, sequentially accessing all data tracks in that region asurface via a corresponding head, before accessing data tracks in asubsequent region of said regions on another surface via a correspondinghead.
 43. In a data storage device having a plurality of storage mediaand a plurality of corresponding data transducer heads, each transducerhead for recording on and playback of information from a correspondingstorage media, a method of defining storage format in one or moreregions on each storage media, wherein each region includes a pluralityof concentric tracks for recording on and playback of information, themethod comprising the steps of: (a) moving each storage media withrespect to the corresponding transducer head and reading data from eachstorage media with the corresponding transducer head; (b) measuring arecord/playback performance capability of each transducer head bymeasuring off-track (OTC) performance of each head; and (c) selecting agroup of track densities, one track density for each region on a storagemedia, based on the measured record/playback performance capability ofthe corresponding transducer head.
 44. The method of claim 43, whereinstep (c) further includes the steps of selecting said group of trackdensities such that each head has maximum off-track capacityperformance, for a required minimum storage capacity for the datastorage device.
 45. The method of claim 43, wherein the step ofmeasuring off-track capacity performance of each head further includesthe steps of measuring the Unsqueezed off-track capacity (UOTC)performance and the squeezed off-track capacity (SOTC) performance foreach head.
 46. The method of claim 45, wherein step (c) further includesthe steps of selecting said group of track densities such that each headhas maximum UOTC performance and maximum SOTC performance, for arequired minimum storage capacity for the data storage device.
 47. Themethod of claim 45, wherein: UOTC=(WW−RW)/2+E+f(BER); andSOTC=TP−SQZ−(WW+RW)/2+f(BER); wherein WW is head write width, RW is headread width, EW is erase width, TP is track pitch, SQZ is squeeze, BER ison-track bit error rate, and f is a function.
 48. A method of testing adata storage device having a plurality of media surfaces, the methodcomprising the steps of: (a) measuring for each media surface, at leastone of a maximum recordable track density of data or maximum recordablelinear density of data; (b) calculating the surface capacity of eachmedia surface from the measured maximum recordable track density ormaximum recordable linear density; (c) summing the surface capacities ofeach media surface to determine a device capacity and qualifying thedata storage device if the device capacity equals or exceeds a desiredcapacity.
 49. The method of claim 48 wherein step. (a) comprises thesteps of: (1) selecting a track density of data and recording data inthe selected track density on the media surface; (2) reading therecorded data and measuring an error rate of the recorded data; and (3)comparing the measured error rate to an acceptable error rate, and ifthe measured error rate is greater than the acceptable error rate,repeating steps (1) to (3) for the selected track density less adecrement, until the error is less than or equal to the acceptable errorrate, to determine a maximum recordable data track density for the mediasurface.
 50. A data storage device prepared for storage of data by themethod of claim 48.